Variable condenser



Mal'h 12 1940- K. F. RonGERs 2,192,985

VARIABLE CONDENSER Filed July 31.. 1957 v F/GJ- 53 /5 /9 5 /3 /o a 6 /9 /4 4 4 L2o f2: La:

/N VEN ron y /c f- Rona/ms A T TORNE Y Patented Mar. 12, 1940 UNITED AS'rpfrls PATENT OFFICE VARIABLE coNpaNsEa xm F. mers, New York, N. Y., signor to Bell Telephone Laboratories,

Incol'lwrated,

New York,' N. Y., a corporation of New York Application .my '31, 1937, serial No. 156,640

Claims.

This invention relates to condensers and more particularly to a variable condenser.

The object of the .invention is to provide an improved variable condenser structure suitable 5 for use where a high precision and a low torque Vlys the rotor set of plates that permits bending or removal of portions of the endmost plates of the rotor set to change the characteristic'of the condenser.

Features in addition to those above mentioned n reside in a low torque and low friction structure and in a wear resisting end-thrust bearing arrangement.

In the drawing and considering that the condenser is in a vertical position:

Fig. 1 is a top plan view of the condenser with a portio'n of the top plate removed;

Fig. 2 is a side elevational view of the condenser, partly in section;

Fig. 3 is a view, partly in section, of a portion of the stator assembly and a supporting means 00 for the stator assembly and taken in the direc- 'tion of the arrows on the line 3--3 in Fig. 1.

Fig. 3 is drawn on an enlarged scale relative to Figs. 1 and 2;

Fig. 4 isa view, partly in section, of another portion of the supporting means for the stator assembly and taken in the direction of the ar- 1 rows on the line l-4 in Fig. l. Fig. 4 is drawn to the same scale as Fig. 3; and

Fig. 5 is a plan view of an electrical connecting means for the rotor assembly and taken in the direction of the arrows on the line 5-5 in Fig. 2. Fig. 5 is drawn on anenlarged scale relative to Fig.`2.'

In variable condensers Where comparatively 1 45 high precision is required it is important .that

the stator and rotor plate assemblies be so set relative to each other that the plate members are in exact parallelism at all times and that this condition of parallelism willl not be changed in service. y

It is also vof importance, particularly in signal translating and transmitting systems, that' the condenser does not operate to produce false signais in the system such, for instance, as might be produced by relatively moving contacts in the condenser.

It is also important in condensers used in systems as above mentioned that the condenser have a low torque so that it may be operated bymeans of a comparatively low power motor such for n- (Cl. F15-41.5)

stance as a motor operating in accordance with changes in the transmission characteristics of a line system, such changes being due, for instance, to changes in atmosphericV conditions.

When a low torquel condenser is used for the I purpose above mentioned, it is also important that there be no residual force in the condenser structure sutlicient to move the rotor of the condenser from a position of rest.

When stop members are provided in the conl0 denser structure to limit the extent of relative movement'v of the plates, it is also important that the impact between the stop members does not cause a change in the setting of the plates.

In this invention: 16

The supporting means for the stator plates are so arranged -that the stator plates may be brought,

' during manufacture of the condenser, into a required position so that they will be in exact parallel spaced relation with the plates of the rotor assembly and without introducing any stresses "which might later tend to cause movement of the stator assembly from the required position.

A coiled conductor is provided as a continuous electrical connection between the rotor assembly and a terminal member. u

The bearings in the condenser with the exception of an end-thrust bearing are merely alignment bearings and have no weight supporting function. The end-thrust bearing carries the entire weight of the rotor assembly and the n contacting surfaces of the end-thrust bearing are of comparatively small areas. Also the cooperating parts of the end-thrust bearing are made of relatively matched and comparatively hard materials to reduce to a minimum both friction and u wear.

Stop means are provided to limit the extent of rotation of the rotor assembly, the stop means having no connection with the stator plates.

With reference to Figs. 1 and 2 of the draw- 0, ing, I and 2 are respectively top and bottom plates of a frame, the plates being held in spaced relation by means of rods 3, 4, 5 and 6. The rods may be square in cross-section and have reduced round end portions 1A extending through u apertures in the plates I and 2 and the outer end portions being spunvover against theouter surfaces of the plates I and 2. The top and bottom plates I and 2 and the rods 3, 4, 5 and 6 serve as a frame structure for supporting ythe stator 5 8 of assembled condenser plates and a rotor 9 of assembled plates.

The stator 8 comprises a plurality of plates I0 of electrical conducting material heldin spaced relation by means of tie bars II, I2 and I3 of conducting material. The tie bars II, I2 and I3 are slotted to receive edge portions of the plates I0 and are in electrical connection with the plates IIL The tie bars II and I2 are located on oppon site sides of the set of stator plates and in cooperation with other elements to be subsequently described serveas supporting means for the stator plates I0. The tie bar `|8 is located at an intermediate offset point between the tie bars I and I2 and serves as an intermediate connector and spacer bar for the plates III.

I have found that it is of some advantage to have the top and bottom end plates of the frame and the statory plates all made of the same material to prevent relative strain or movement of these parts under changes in temperature since such changes would in some instances cause disalignment of the stator plates.

The rods 8 and 4 serve to hold the top and `bottom plates and 2 of the frame in spaced relation. 'I'he rods 6 and 6 serve to hold the top and bottom plates I and 2 of the frame in spaced relation and also serve as part of the supporting means for the stator 8. I'he vrods 6 and 6 are transversely drilled and tapped to receive respectively screws |4|4 and IS-II. The screws Il-Il as shown in Figs. 1 and 4 extend through an apertured slab I6 of insulating material and enter the rod 6. 'Ihe apertures |1-I'I in the slab I6 are larger in diameter than the diameter of the shank portion oi.' the screws |4|4. A anged bushing |8 adapted to receive the shank portion of a screw I4 is located in each aperture I1 and directly beneath the head of the screw. The flangev of the bushing is interposed between the head of the screw and the outer surface of the slab I6. 'I'he bushings I8 may be made of comparatively soft metal or insulating material and serve as cushioning means between the screws Il and the apertured slab I6 of insulating material to prevent fracture of the slab I6 when the screws Il are tightened and also serve as bushings between the shank portions of the screws and the apertured portions of the slab to prevent lateral movementof the slab. An

`apertured strip |9 of comparatively soft metal or insulating material is interposed between the inner face of the slabl I8 and the outer face of the rod 6 to further protect the slab I6 from fracture when the screws Il are tightened. The slab I8 and the apertured strip I9 are held tightly pressed against the outer face of the rod 8 by means of the screws |4|4, the strip I9 being interposed between the slab I8 and the rod 6. To insure securement of the screws |4-I4 in the threaded apertures inthe rod 6, I have found it preferable to apply a small quantity of solder to the threaded ends of the screws and to the adjacent apertured portion of the rod 6. apertured slab 2|) of insulating material is supported by the screws I5 as shown in Fig. l against the rod 5 in the same manner as the slab I6 is supported by the screwsv Il--II against the rod 6. 'Ihe slabs I6 and 2|) of insulating material are identical in structure and provide insulating supporting means for the stator 8.

Spaced apertures 2| are provided in the free end of slab I6 as shown in Fig. 3 and the free end of slab I6 is provided with a metallic coating 22 as shown in this ilgure and in Fig. l. The coating 22 is applied to the outer face of the slab I6,\adjacent the apertures 2| and to the inner surfaces of the apertures to provide a coating of y strongly adherent solderable material around and within the apertures. The metallic coating may be applied by spraying the free end of the slab |6with a metallic compound and firing at a comparatively high temperature or may -aies-:,986

be applied in any other manner found practicable. I have found that silver may be readily applied to the slab I6 and that this metal provid a strongly adherent solderable coating. The metallic coating 22 is applied to the slab I6 to provide a metal surface to which studs 23 of the stator assembly may be joined by means of solder or other comparatively low melting point metal. 'I'he studs 23 are male threaded on one end tc enter drilled and tapped holes 2l in the tie bar as shown in Fig. 3 and have outer ends adapted to enter the apertures 2| in the slab I8. The outer ends of the studs 23 may be made hexag- 4onal in cross-section to facilitate turning of the studs 23 into the drilled and tapped holes 24 in the tie bar II. 'Ihe apertures 2| in the slab Il of insulating material are much larger in diameter than the diameter of the stud 2l.

When the stator assembly 8 is being mounted in the structure, the stator assembly is placed precisely in position and held in this position by means of a suitable jig. 'I'he slab I6 is then secured to the rod 6 by the screws II--II as described above. Molten metal is then flowed around the unthreaded ends of the studs 23 and into the apertures 2| in the slab I6 of insulating material and over adjacent portions of the metal coating 22. A suiilcient quantity of molten metal is applied in the apertures 2| and around the unthreaded ends of the studs 23 and over the adjacent surfaces of the metal coating 22 to hold the stator assembly in required position when the metal cools. 'I'he hexagonal shape of the studs 2,3 in addition to facilitating turning of the studs into the tapped holes in the tie bar also assists in flowing the metal of the jointure into the excess space in the apertures. 'I'he molten metal when cooled forms a cap 25 closely embracing and also adhering to the unthreaded end of the stud 23 and adhering to the metal coating 22 on the slab I6 of insulating material. I have found it necessary for this condenser which is for exacting service to use a metallic coating on the insulating slab. However, with careful flowing in or casting of metal on the studs and in the apertures, it would not be necessary to coat the insulating support in all cases. The arrangement above described provides a means for mounting one side of the stator assembly cn-the slab I6 of insulating material. The opposite side of the stator assembly is mounted on the slab 20 of insulating material in a similar manner, the slab 20 being apertured on its free end to receive studs 26 of like form to the studs 23 and the slab 28 having a coating 21 vof metal on its free end. 'I'he studs 26 are threaded into threaded holes in the tiebar I2 and the unthreaded ends of the studs 26 are anchored to the coating 21 of metal on the slab 20 by means of caps 28. The caps 28 are formed by ilowing metal around the unthreaded ends of the studs 26 and within the apertures in the free end oi' the slab 20 and over adjacent surfaces of the coating 21. A terminal 29, such for instance as a. suitable length of bare stranded wire, is applied to one of the studs 26 and has an end portion embedded! in the respective cap 28. Since it is common practice to connect a circuit wire to a terminal by soldering the parts together, it is preferable that the metal used in forming the caps 28 be of a higher melting point than the common run of solder used in making connections between a wire and a terminal so that the material of the caps 28 will not be softened by the heat applied during the soldering of the circuit wire to the terminal and there will beno consequent shifting of the s tator assembly during the soldering operation. It is to be noted that the coatings 22 and 21 of metal on the respective slabs I6 and 20 of insulating material do not extend over the whole surface of the slabs but are only on the end portions `in which the studs 2land 25, respectively, are secured. The slabs Il and 2II of insulating material, therefore, insulatingly support the stator assembly in the frame.

The rotor 9 comprises a set of spaced plates Il supported in spaced relation on an annularly grooved metal sleeve 2l, supported on a rotor shaft l2 and held thereto by means oi' set screws 33. The rotor shaft I2 is journaled in bearings 34 and l5 mounted on the respective end plates I and 2 of the frame, the bearings being secured to the end plates by means of screws 26. An adjustable end-thrust bearing 31 screw-threaded into a ring 38, secured to the end plate 2, supports the weight of the rotor l. `The structure of the end-thrust bearing and its function will be subsequently described. A

The metal sleeve Il of the rotor 9 is electrically connected to the frame of the condenser by means of a coiled ribbon 3Q of conducting material. The ribbon 39 is coiled in the form of a flat spiral as shown in Fig. and encircles the rotor shaft 32. The inner end of the ribbon 29 is secured to a metal pin 40 which, as shown in I! tion which would introduce torque in operation or tend to cause rotation of the rotor assembly when at rest. 'I'he plane of the spiral is horizontal and the ribbon 39 is arranged to provide a large section modulus or stiil'ness against vertical deformation with the least stiffness toward horizontal operating forces. A terminal 42 secured to the end plate 2 by means of a screw 43 is provided so that a circuit wire may be electrically connected to the frame. The ribbon 39 provides a continuous electrical connection between the rotor and the frame at all times and eliminates all chance of the development of false signals such as are produced for instance by sliding contacts.

Each plate 3l of the rotor 9 has'a projection 44 near the outermost end portion as shown inFig. 1. The projection 44 extends inthe same plane as the plate III and from the straight edg'eportion of the plate. The projection 44 is recessed to provide spaced n'ger portions 45`-45. The y linger portions 45-45 extend into an annular lgroove in a stop bar 46 and are held 'in the annular groove by soldering the parts together or by connecting the parts in any otherl manner found practicable for securement of the parts. The stop bar 46 is annularly grooved at spaced intervals to receive the finger portions v45--45 of the rotor plates 30 and holds the outermost end portionswof the rotor platesin spaced relation. The finger portions 45--45of the endmost rotor plates extend around reduced end portions 4'I-4I of the stop bar and are not connected to the stop bar 4B but are left free. arrangement whereby the endmost plates of the rotor assembly may be warped toward or away This provides an from the adjacent stator plates to slightly vary the characteristic of the condenser, or the free end portions of these outermost plates of the rotor may be reduced in area as required for the same purpose. The reduced end portions 41-41 of the stop bar 46 extend beyond the ends of the rotor assembly and normal to the planes of the rotor plates and almost to the inner surfaces of the-end plates I and 2 of the frame. Filister head screws 48-48 are screw-threadedly supported in the endplates I and 2 of the frame in the path of. movement of the end.- portions 41.-" of the stop bar 46. v The end portions 41-41 of the stop bar46 engage the head portions of 'the screws 4l when the rotor 9 of the condenser `is rotated to bring substantially all portions of the rotor plates 30 into interleaving relation with the plates III of the stator and stop further rotation ofthe rotor 9.in this direction. The iilister head screws 4848, therefore, serve as stops for the stop bar 46. The same object could be attained by slotting the end plates I and 2l and extending -the stop bar 46 to extend into the slots. Since the stop bar 46 is carried by the rotor plates 30 and the screws 48-48 are mounted in the end plates I and 2 of the frame, there is no impact between the rotor 8 andthe stator I0 but only impact between the rotor and the stops in the end plate of the frame. This arrangement prevents driving of the stator assembly from its adjusted positionor fracturing of the slabs I6 and 20 of insulating material. The slabs I6 and 20, therefore, may be made of porcelain or other like frangible insulating material or of fibrous insulating material and the studs 23 and 26 of the stator assembly may be'safely mounted in caps and 28 of solder or other comparatively soft metal without danger of having the position of the stator changed by impact of the rotor. 1

When the rotor is movedto bringvthe rotor plates out of interleaving relation with the stator plates III, for instance in a clockwise direction from the position shown in Fig. 1, the extent of rotation in this direction is limited by the rod 4. The rod 4 as indicated in Fig. 1 is not' located at the lower left corner of the irame but is located above the lower left corner and between the lower left corner and the slab 20 of insulating material to permit sufllcient rotation of the rotor plates to bring therotor plates entirely out of interleaving relation with the stator plates. The rotor cannot be rotated in -a clockwise direction to such an extent as to bring the rotor assembly into engagement with the slab 20 since it is stopped by means of the rod 4. Since the rotor cannot be moved-to'strike the slab 20 or any of the portions of the statorv supported thereby,

there is no danger of Vthe slab 2.0 of insulating material'being fractured or of the stator being driven fromI its position.

The condenser shown and described is adapte-d to be operated in the position shown in Fig. 2,

that is, with the rotor shaft 32 in la vertical position. In this position, the weight of the rotor assembly is carried by the end-thrust bearing 31. The end-thrust bearing 31 may be turned to a greater or less extent within the internally threaded ring 38 to raise or lower the rotor assembly as required to obtain correct spacing of the rotor plates relative to the stator plates. A

` lock nut 49 is provided on the end-thrust bearing 31 to prevent. accidental turning of the endthrust bearing 31. The end-thrust bearing 31 is made hemispherical on its upper end and is highly polished at this -point and engages an insert 50 in the lower `end oi the rotor shaft 32. The insert 50 is made of material about equal to the hardness of the end-thrust bearing l1 to prevent undue wearing away of the parts. The

portion of the insert-50 engagedby the heini-` spherical end of the bearing 3l is made ilat to reduce to a minimum the area o! Contact between the parts. The ilat portion of the insert is also highly polished.v The structure, therefore, is a very low friction point bearing.

The condenser may be enclosed in a casing, not shown, with the rotor shaft extending through a wall or panel of the casing. Internally threaded spaced rings 5i, 52 and 53 are supported on the upper surface of the end plate l of the frame to receive mounting screws, not shown, but which may extend through the wall or panel of the casing.

The rotor of the condenser may be rotated by means ofa motor or manually by means of a knob. the motor or knob being connected to the rotor shaft `32. Since the particular means employed for rotating the rotor does not form part of the invention, no showing is made of such means.

Although the condenser has been described as being in a vertical position as' shown in Fig. 2 is is obvious that the condenser may be set in a horizontal position and that if used in this position means may be provided in the structure for holding the rotor assembly against the endthrust bearing. l 4

Although in order to disclose the invention a particular structure has been shown and described. it is to be understood that certain changes may be made in the structure without departing from the spirit of the invention. For instance, it may be found preferable to support the slabs I6 and 20 at both ends by the identical means shown in Fig. 3 and described above. To do this the stator assembly 8 will be rigidly and precisely located with relation tb the frame, the

slab I6 will be placed in position on the four` studs 23 and molten metal will then be flowed into the apertures in the slab i6 and over the adjacent portion of the metal coatings 22. In

this arrangement the two apertured ends of the slab I6'will have metallic coatings, the coatings being separated by an uncoated area to insulatingly separate the ends. I

What is claimed is:

1. In a variable electrical condenser, a frame comprising spaced plates and rods extending transversely of said spaced plates,y apertured slabs of frangible insulating material supported on the rods of said frame and having apertured free end portions, cushioning means interposed 1 n between said slabs and said rods, metal coatings of frangible insulating material supported on the rods of said frame and having apertured tree end portions, screws extending through said slabs and into said rods, cushioning strips interposed between said slabs and said rods, and flanged tubular cushions interposed between the head portions of said screws and said slabs to prevent fracturing of. said slabs, metal coatings on the free end portions of said slabs and'surrounding and extending into the apertures therein, a set of stator plates,.tie bars connected to said stator plates, studs on said tie bars, said studs extending into the apertures in the free ends of said slabs and capsof metal embracing said studs in the respective apertures and adhering to the metal coating on said slabs.

3. In a variable electrical condenser, a frame comprising end plates and rods extending transversely o! said end plates and secured thereto, apertured slabsof frangible insulating material clamped to said rods and having apertured free end portions, screws extending through said slabs and into said rods, strips of relatively soit metal interposed between said slabs and said rods, relatively soft metal flanged tubular members disposed in apertures in said slabs and interposed between said screws and said slabs to prevent fracturing of said slabs by means of said screws, a coating of metal on the free end portions of saidslabsj, said coating surrounding the apertures in the free end portions of said slabs, a set of stator plates, tie bars connected to saidstator platesand extending transversely of said stator plates, studs on said tie bars extending loosely into the apertures in the free end portions of said slabs and caps of solder embracing said studs within the apertures in said slabs and connected to said coating of metal.

4. In a variable electrical condenser, a frame, an apertured slab of ceramic insulating material supported by said frame, a cushioning strip interposed between said slab and said frame, a set of stator plates, a tie bar attached to said stator plates and holding said plates in spaced relation, studs mounted in spaced relation on said tie bar, polygonal head portions on said studs projecting into apertures in said slab, caps of low melting point metal extending through apertures in said slab and embracing said head portions of said studs and enlarged button-like head portions on said caps extending over portions oi' said slab.

5. In a variable electrical condenser, a frame,-

an apertured slab of ceramic insulating material supported at one end by said frame, a strip of cushioning material interposed between said slab and said frame, a coating of metal on the unsupported end portion of said slab, a set of stator plates, a tie bar attached to said stator plates and holding said plates in spaced relation, studs mounted in spaced relation in the side of said tie bar, hexagonal head portions on said studs projecting into apertures in said slab, caps of low melting point metal extending through said slab and embracing said head portions of said studs and enlarged button-like head portions on said caps extending over portions of said coating of metal on said slab and adhering to said coating of metal.

KARL F. RODGERS. 

